Question about the Wait Function

Question

I wrote a VI to store the time stamps in a text file.
I fond something strange in the text file (see the picture below).
The time stamps weren't writen into the file every 10 ms! How could this happen? And how could I fix it and make the time stamp to be writen every 10ms?
Thanks a lot!

Answer 1

To further what was just said:
The wait function will indeed wait 10ms, or near enough as I will soon explain.
When used in a loop, the wait function will wait for 10ms AFTER the code inside the loop has been executed.
Depending on your Operating System, and the speed of your PC, the code inside the loop could take several hundred milli-seconds to execute.
So the total time for each loop iteration, and thus the time between file writes, will be (Xms + 10ms), where X is the time taken to execute the other code.
Another thing to consider is that unless you are using a Real-Time OS, your Windows or Mac OS will not prioritise LabVIEW! The execution of your code must run alongside your virus scanner, email client, music player etc. etc. etc.
As such, it is often asking too much to try to use labVIEW in accuracies of +/-1ms on the common desktop PC.
As a final note: I cannot give facts on file writing, but just from my experience with LabVIEW a file write every 10ms is impractical as the write-to-file VI usually takes longer than 10ms to execute itself. Why not buffer up 10 writes/pieces of data/whatevers and then write them all to file at once? Whilst we are at it, why not buffer 100 pieces and then write them all at once?
I have had this idea argued before, with people saying that if the system were to crash then the buffered up 100 reads would be lost. Remember guys: that labVIEWs write to file VI passes the data to the windows write buffer, and windows doesn't necessarily put it on disk straight away! That can only be guaranteed by closing the file reference or flushing the queue.
Apologies, I have diverged.
Rhys
Applications Engineer
National Instruments